The statements in this section merely provide background information related to the present disclosure and may not constitute the related art.
Recently, efforts to extend an application range of a wound rotor synchronous motor have been made due to the mineralization of rare earth resources and rise of manufacturing costs and supply crunch of rare earth permanent magnet materials.
For example, an interior permanent magnet synchronous motor (IPMSM) has been used as an electric motor (driving motor) as a driving source of an eco-friendly vehicle but research and development to apply a wound rotor synchronous motor (WRSM) having a rotor and a stator with winding coils as a driving source of an eco-friendly vehicle has actively proceeded.
As is well known, a wound rotor synchronous motor is a motor for applying an electric coil instead of a permanent magnet to a rotor and is configured to generate torque according to interaction with a stator by winding a coil around the rotor and applying direct current (DC) to the coil to form an electric field.
As described above, the wound rotor synchronous motor with the rotor being wound by a coil instead of a permanent magnet additionally requires control of rotor current If flowing through the rotor coil and, thus, when a conventional control method of a permanent magnet synchronous motor is used, overload of a control central processing unit (CPU) and massive map data due to a combination of a control variable of vector control currents Id and Iq and rotor current If may occur
In addition, force corresponding to magnetomotive force of a permanent magnet needs to be generated as electromotive force of a rotor through input of DC current in a wound rotor synchronous motor and, thus, heating and temperature rise frequently occur due to copper loss of a rotor coil.
Accordingly, when a wound rotor synchronous motor is applied, a temperature of a rotor wound by a coil increases and, thus, a technology of estimating a rotor temperature is desired.
When logic for preventing temperature rise of a rotor coil and protecting the rotor coil according to a load operating condition is not applied, copper loss of the rotor coil and limit in operating performance may occur.
In particular, excessive heat may be generated in a wound rotor synchronous motor due to loss of a rotor according to a load operating condition. Accordingly, there is a possibility of degradation in motor performance due to reduction in magnetic flux of a rotor and loss in a rotor coil occurs and a possibility of a fire breaking out because a rotor overheats.
According to the related art, a logic for preventing temperature rise of a rotor coil and protecting the rotor coil based on an actually measured temperature of the rotor coil for each operating condition is configured by storing actually measured values for each current according to an operating condition/stator in the form of a database to configure a rotor coil current control map and then inducing optimum rotor current of an existing input variable from the rotor coil current control map.
However, an exaggerated rotor coil current control map due to an excessive combination of control variables of vector control currents Id and Iq, rotor current If, and so on and reduction in processing velocity due to overload of a control CPU may be caused.
In addition, an excessive amount of data and excessive time taken to store coil temperature of a coil for each rotor current in the form of a database in order to inhibit loss in a rotor coil may be caused.
Accordingly, although a technology for estimating a temperature of a rotor coil according to a rotor temperature table based on an interpreted value has been known, it is not possible to accurately measure the temperature of the rotor coil according to a real-time operating condition.
As a result, reduction in control performance of a wound rotor synchronous motor due to a deviation in temperature measurement may be caused. Also, design criteria for protection of a rotor from overheating may not be accurate, and additional expenses for storing data may be incurred.
It is difficult to accurately estimate a temperature of a rotor coil and, thus, there are severe problems in terms of reduction in performance of a wound rotor synchronous motor due to loss in resistance and a fire risk due to loss in a rotor coil.